This invention relates to a splitter plate arrangement for a flue gas stack.
Power generation facilities and numerous other facilities which produce fossil fuel combustion gas emissions including pollutants typically comprise a vertical flue gas or exhaust stack through which the exhaust gases are flowed to be released to the atmosphere. The levels and characteristics of such released gas emissions often must be in accord with statutory or regulatory limits. Thus, it can be understood that accurate and repeatable determinations must be made concerning the emission levels and characteristics so that compliance with the statutory or regulatory limits can be assured.
One commonly measured emission characteristic which relates to the pollutant contribution of a flue gas emission is the flow rate of the flue or exhaust gas through the stack. However, accurate measurement of the flue gas flow rate is complicated by the flow pattern of the flue gas in the stack and the configuration of the flue gas flow path at the entrance of the stack significantly influences this flow pattern. The flow patterns in cylindrical flue gas stacks formed by the flow of the flue gas from a horizontal or near horizontal duct into the stack can best be described by two counter-rotating vortices within the stack. These vortices are unstable and interact with each other as the flue gas travels up the stack in a spiral pattern. The swirling flow in the stack is controlled by one of the two counter-rotating vortices. Flow instabilities can result in a momentary change in direction of the swirl as the opposing vortex gains control.
Thus, the gas flow in the exhaust stack is often turbulent and has a rotating component. These factors complicate the task of accurately measuring the gas flow rate by a Pitot or other pressure type probe.
Moreover, the flow pattern in the exhaust stack can result in pressure pulsations which travel back through the plant equipment which is upstream of the exhaust stack. This can have an adverse effect on the operation and structural integrity of the process and equipment. As one example, combustion gas turbines are often used to provide electric power usually for standby or peaking power. Because the thermal efficiency of gas turbines alone is rather low due to the high exit gas temperature, the gas turbine is most often combined with a heat recovery steam generator and a steam turbine to produce additional electricity. As a combination of a gas turbine cycle and a steam turbine cycle, these systems are referred to as xe2x80x9ccombined cyclesxe2x80x9d. Gas turbines with heat recovery steam generators are also used to produce process steam in co-generation plants.
In the situation of combined cycles or co-generation, the pressure pulsations previously referred to travel upstream through the heat recovery steam generator and through the inlet duct to the interface with the gas turbine. Although the interaction of the pressure pulsations with the gas turbine are not fully known, it is hypothesized that the pulse is reflected off of the rotating blades of the turbine and then travels back downstream. Measurements have shown that the turbine back pressure can vary as much as 10% depending on the amplitude of the pulse. Of course, such a large variation in back pressure can have a negative impact on the operating stability of the gas turbine. Furthermore, such pressure swings can have long term risks associated with material fatigue and stress. These same operating and structural problems will also exist to varying degrees with combustion equipment other than combined cycle systems.
An additional benefit of the splitter plate arrangement, as demonstrated in laboratory tests, is the reduction in the pressure drop between the inlet or breech and the exit of the stack. The reduction of the pressure drop reduces fan power consumption and thereby increases the overall efficiency of the power plant by reducing parasitic power consumption.
Accordingly, deductive reasoning draws the conclusion that, if the accuracy and repeatability of flue gas flow rate measurement could be improved, the reliability of reported flow rates would be improved. Furthermore, the operators of power generation facilities and other emission producing facilities could plan their operations with more confidence and efficiency in reliance upon the accurately measured flue gas flow rates. Moreover, it would be advantageous if any approach which yields an improvement in measuring flue gas flow rates also yields other benefits such as reducing flow instabilities which can have an adverse effect of the operation and structural integrity of the process or equipment and can reduce, in most cases, the gas pressure loss through the stack.
It is, therefore, an object of the present invention to provide a new and improved splitter plate arrangement which sets up conditions within a flue gas exhaust stack such that an accurate and repeatable measurement of the flue gas flow rate can be obtained.
It is a further object of the present invention to provide such a new and improved splitter plate arrangement which is characterized by its capacity to reduce flow turbulence and pressure drop in a flue gas exhaust stack as compared with conventional splitter plate arrangements.
In accordance with one aspect of the present invention, there is provided a splitter plate arrangement for a flue gas stack. The splitter plate arrangement controls the flow of flue gas in a vertical stack having an annular entry communicated with two inlets both disposed on a common inlet axis which bisects the annular entry into two bisected halves, the two inlets being oriented in opposition to one another such that the inlet flows of flue gas through the opposed inlets are in opposed directions to one another. The splitter plate arrangement includes a first splitter plate and a second splitter plate. The first splitter plate extends radially inwardly from the inner surface of the vertical stack at generally the midpoint of one bisected half of the annular entry of the vertical stack on one respective side of the inlet axis. The second splitter plate extends radially inwardly from the inner surface of the vertical stack at generally the midpoint of the other bisected half of the annular entry of the vertical stack on the other respective side of the inlet axis.
According to further features of the one aspect of the present invention, the first and second splitter plates each have a radial extent of between about twenty-five percent (25%) to fifty percent (50%) of the radius of the annular entry of the vertical stack. Also, the first and second splitter plates each have a vertical extent greater than the vertical extent of the inlets.
According to yet additional features of the one aspect of the present invention, each inlet is formed as a quadrilateral opening. Also, the first and second splitter plates are each quadrilateral in shape.
In a variation of the one aspect of the present invention, the respective pair of ducts entering the stack are at an included angle which is other than one hundred and eighty (180) degrees such as, for example, one hundred and fifty (150) degrees or less.